In modern Code Division Multiple Access (CDMA) systems soft handover or handoff is a preferred method for transferring support for a mobile communication unit from one base station to another as the communication unit moves between cells within, for example, a Radio Access Network (RAN). Since CDMA systems use the same frequencies between cells it is possible to make new connections with base stations while existing connections are maintained reducing power requirements, interference and the like and decreasing the probability of a dropped call.
In making handoffs or handovers, the communication unit maintains what is referred to as an Active Set associated with base stations to which service for the call in progress can be transferred if certain handoff parameters are met based on measurements of pilot signals from various base stations within range. The measurement process is ongoing and the handoff parameters include pilot strength thresholds that cause, for example, the base station to be added to the Active Set or dropped from the Active Set. In conventional systems, the handoff parameters typically used to allocate channels are provided to the mobile on the basis of a single RC, typically RC1 which is used throughout the RAN regardless of whether or not different radio configurations are possible. For example, for CDMA2000 or IS-2000 based RANs a multitude of RCs are available. Disadvantageously however, in CDMA2000 or IS-2000 systems, handoff parameters are set system-wide as noted based on, for example, RC1 and are the same regardless of the existence of the additional radio configurations.
It should be appreciated by one of ordinary skill in the art that handoff performance depends on link budget. Further, link budget performance of a RC in a CDMA2000 or IS-2000 system varies depending upon prevailing conditions and, for example, the type of modulation and coding applied for a particular RC. For example, in a typical CDMA2000 or IS-2000 system, RC2 has less channel gain than RC1 by 1.8 dB. Other RCs have divergent gains, with some RCs having more and some having less. It will be appreciated that higher channel gain requires less Ec/Io for adequate demodulation and thus some RCs may have gains particularly well suited for demodulation.
However, since as noted, in CDMA2000 or IS-2000 systems, handoff parameters are set system-wide based on a standard RC such as RC1, the ability to operate using handoff parameters associated with other, often more optimum radio configurations, is limited leading to, for example, limited Active Set candidacy for base stations which might otherwise be more desirable candidates than candidates chosen based on handoff parameters associated with the standard RC.